The role of Rhizobial exopolysaccharides and carbohydrate-signaling molecules in root hair attachment and nodule construction in symbiotic nitrogen fixation is being studied by Dr. Graham Walker. An exopolysaccharide, called succinoglycan, which is a high molecular weight polysaccharide consisting of octasaccharide units has been characterized by Dr. Reinhold using ESI-MS/CID mass spectrometry. The specific locations of acetyl, succinyl and pyruvyl groups, on the octasaccharide subunit are critical for function and these were assigned by Reinhold's group. In addition it was shown that R.meliloti mutants can synthesize a second exopolysaccharide (EPS II) that is capable of substituting for the role of succinoglycan. Dr. Walker has cloned and sequenced nineteen exo genes that affect the synthesis of succinoglycan and in addition has been able to assign biochemical roles to their gene products. Genetic studies of EPS II biosynthesis are in progress and multiple new EPS II variants will require characterization. New succinoglycan derivatives that are available in only trace amounts and that would normally be set aside will instead be submitted to Dr. Reinhold for mass spectrometry characterization.